Method for making wallboard or backerboard sheets including aerated concrete

ABSTRACT

A method for making wallboard or backerboard sheets which are relatively lightweight, strong, and which have good fire resistance, thermal insulation, and sound absorbing properties includes forming core material having opposing first and second major surfaces and comprising aerated concrete, securing at least one face layer on at least one of the first and second major surfaces of the core material, and cutting the core material and at least one face layer secured thereto into a plurality of wallboard or backerboard sheets. The provision of aerated concrete for the core provides many key advantages over conventional gypsum wallboard sheets, and/or conventional backerboard sheets, such as gypsum greenboard or cementitious backerboard, for example. In one class of embodiments, the method may further include curing the core material prior to securing the at least one face layer thereto. In another class, the method may further include curing the core material after securing the at least one face layer thereto.

RELATED APPLICATION

[0001] The present application is based upon U.S. provisional patentapplication serial No. 60/158,172 filed Oct. 6, 1999, the entiredisclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to the field of manufacturingconstruction products, and, more particularly, to methods for makinglightweight, high-strength, fire-resistant wallboard sheet, and/ormoisture-resistant backerboard sheets.

BACKGROUND OF THE INVENTION

[0003] Wallboard sheets are widely used in building construction to formpartitions or walls of rooms, elevator shafts, stair wells, ceilings,etc. The sheets are typically fastened to a suitable supportingframework. The seams between sheets are covered to provide an even wallsurface. The sheets may be readily cut to size by first scoring the facesheet, and then snapping the board about the score line. The wall maythen be painted or covered with a decorative wall covering, if desired.Such wallboard sheets created from a gypsum core with outer face layersof paper, sometimes referred to as gypsum board or drywall, are wellknown.

[0004] Gypsum wallboard is typically manufactured by delivering a slurryor paste containing crushed gypsum rock onto a moving sheet of facingpaper to which a second or top paper layer is then added to form a longboard line. The board line permits the slurry to harden before beingcut. The cut panels are heated in a kiln, before being packaged forstorage and shipping.

[0005] Typically, such sheets are ½ or {fraction (5/8)} inch thick andin conventional sizes of 4×8 feet, such a gypsum wallboard sheet mayweigh about 55-70 pounds. Accordingly, handling of such gypsumwallboards presents a significant task for construction personnel orwallboard “hangers”, particularly when such boards are secured overheadto form a ceiling. In addition, the fire resistance, thermal insulationand sound absorbing properties of conventional gypsum wallboard sheetsmay not be sufficient for some applications.

[0006] Another variation of gypsum wallboard is water-resistant drywallor “greenboard”. The greenboard typically includes the same gypsum core,but includes a water-resistant facing so the water is less likely topenetrate, stain and/or decay the wall. Greenboard is typically used forwalls in a moist or humid environment, such as a bathroom, for example.Such greenboard is not typically recommended as an underlayment for tilein the bathroom, for example, since water may penetrate the grout orcracks between adjacent tiles and deteriorate the greenboard. U.S. Pat.No. 5,552,187 to Green et al. discloses the addition of a fibrousmat-faced gypsum board coated with a water-resistant resinous coatingfor greater durability in moist environments.

[0007] Yet another related conventional wallboard product to serve as anunderlayment for wet areas is the concrete backerboard. For example,UTIL-A-CRETE® Backerboard from Bonsal is a precast cementitiousbackboard with glass mesh reinformcement. The board includes portlandcement, fiber glass mesh and lightweight aggregate. The backerboard ismore adapted to be used in areas subject to splashing or high moisture.

[0008] While the glass mesh face layers are typically secured to thesurface of the backerboard after the core has been precast, continuousproduction is also disclosed in U.S. Pat. No. 5,221,386 to Ensminger etal. In addition, the mesh or reinforcing layers have also been embeddedin the faces and edges of the backerboards.

[0009] Unfortunately, conventional cementitious backerboards may be moredifficult to score and break to size. Moreover, since the backerboardsinclude a core of cement, their density is considerably greater thaneven conventional gypsym wallboard. Accordingly, manufacturers may offerthe backerboards in smaller sizes to be more readily handled by theinstaller, but such increases seams between sheets and also increasescosts of installation. A typically-sized 4 foot by 8 foot sheet canweigh well over 100 pounds, which is very unwieldy especially inconfined spaces.

SUMMARY OF THE INVENTION

[0010] In view of the foregoing background, it is therefore an object ofthe invention to provide a method for making wallboard or backerboardsheets which are relatively lightweight, strong, and which have goodfire resistance, thermal insulation, and sound absorbing properties.

[0011] This and other objects, features and advantages in accordancewith the present invention are provided by a method comprising formingcore material having opposing first and second major surfaces andcomprising aerated concrete, securing at least one face layer on atleast one of the first and second major surfaces of the core material,and cutting the core material and at least one face layer securedthereto into a plurality of wallboard or backerboard sheets. Theprovision of aerated concrete for the core provides many key advantagesover conventional gypsum wallboard sheets, and/or conventionalbackerboard sheets, such as gypsum greenboard or cementitiousbackerboard, for example.

[0012] In one class of embodiments, the method may further comprisecuring the core material prior to securing the at least one face layerthereto. In another class, the method may further comprise curing thecore material after securing the at least one face layer thereto.

[0013] In one particularly advantageous embodiment, forming the corematerial comprises dispensing materials for making aerated concrete intoa mold and allowing the materials to rise and stiffen into a body,curing the body, and dividing the cured body into a plurality of curedsheets to serve as the core material. The plurality of the cured sheetsmay be joined together in end-to-end relation while advancing the curedsheets along a path of travel. In addition, securing the at least oneface layer may be performed while the cured sheets are advanced alongthe path of travel.

[0014] In another embodiment, forming the core material comprisesdispensing materials for making aerated concrete into a mold andallowing the materials to rise and stiffen into a body, dividing thebody into a plurality of uncured sheets, and curing the sheets to serveas the core material. This embodiment may also include joining theplurality of the cured sheets together in end-to-end relation whileadvancing the cured sheets along a path of travel. Additionally, the atleast one face layer may also be secured while the cured sheets areadvanced along the path of travel.

[0015] In yet another embodiment, forming the core material comprisesdispensing materials for making aerated concrete into a mold andallowing the materials to rise and stiffen into a body, and dividing thebody into a plurality of uncured sheets to serve as the core material.In this embodiment, curing of the uncured sheets occurs after securingthe at least one face layer thereto. Curing may also be performed aftercutting. A high temperature resistant face layer may be required wherecuring is performed after securing of the one or more face layers.

[0016] In accordance with still another embodiment of the invention, themethod includes mixing and dispensing the materials for making aeratedconcrete in slurry form, and wherein securing the at least one facelayer comprises receiving the aerated concrete in slurry form thereon asthe at least one face layer is advanced along a path of travel. Thisembodiment may also include permitting the aerated concrete material torise and stiffen, and curing the liquid aerated concrete after risingand stiffening. The curing may also be after cutting.

[0017] The securing the at least one face layer may comprise securingfirst and second face layers on respective first and second majorsurfaces of the core material. The at least one face layer may comprisepaper, such as for a wallboard. Alternately, the at least one face layermay be moisture-resistant for a backerboard.

[0018] The method may also include forming the first major surface ofthe core material to have beveled portions adjacent respective opposinglongitudinal side edges. Securing the at least one face layer mayinclude securing the at least one face layer to extend around theopposing longitudinal side edges. In addition, forming the core materialmay comprise forming the core material with reinforcing fibers in theaerated concrete.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a schematic view of a portion of a wall structureincluding the wallboard and/or backerboard in accordance with thepresent invention with various layers removed for clarity ofexplanation.

[0020]FIG. 2 is a perspective view of a wallboard sheet as can be usedin the wall structure of FIG. 1.

[0021]FIG. 3 is an enlarged cross-sectional view through a side edge ofthe wallboard sheet as shown in FIG. 2.

[0022]FIG. 4 is a perspective view of another embodiment of a wallboardsheet as can be used in the wall structure of FIG. 1.

[0023]FIG. 5 is an enlarged cross-sectional view through a beveledportion of the wallboard sheet as shown in FIG. 4.

[0024]FIG. 6 is a perspective view of a backerboard sheet as can be usedin the wall structure of FIG. 1.

[0025]FIG. 7 is an enlarged cross-sectional view through a side edge ofthe backerboard sheet as shown in FIG. 6.

[0026]FIG. 8 is a perspective view of another embodiment of abackerboard sheet as can be used in the wall structure of FIG. 1.

[0027]FIG. 9 is an enlarged cross-sectional view through a beveledportion of the backerboard sheet as shown in FIG. 8.

[0028]FIG. 10 is a flowchart for a first embodiment of a method formaking wallboard and/or backerboard sheets in accordance with theinvention.

[0029]FIG. 11 is a flowchart for a second embodiment of a method formaking wallboard and/or backerboard sheets in accordance with theinvention.

[0030]FIG. 12 is a flowchart for a third embodiment of a method formaking wallboard and/or backerboard sheets in accordance with theinvention.

[0031]FIG. 13 is a flowchart for a fourth embodiment of a method formaking wallboard and/or backerboard sheets in accordance with theinvention.

[0032]FIG. 14 is a schematic block diagram of a system for makingwallboard and/or backerboard sheets in accordance with the invention.

[0033]FIG. 15 is a more detailed schematic diagram of a formerembodiment for the system as shown in FIG. 14.

[0034]FIG. 16 is a more detailed schematic diagram of an alternativeportion of the former embodiment as shown in FIG. 15.

[0035]FIG. 17 is a more detailed schematic of another former embodimentand variation thereof for the system of FIG. 14.

[0036]FIG. 18 is a more detailed schematic of still another formerembodiment and variation thereof for the system of FIG. 14.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] The present invention will now be described more fullyhereinafter with reference to the accompanying drawings, in whichpreferred embodiments of the invention are shown. This invention may,however, be embodied in many different forms and should not be construedas limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the invention to thoseskilled in the art. Like numbers refer to like elements throughout, andprime and multiple prime notation are used in alternate embodiments toindicate similar elements.

[0038] The present invention is based, at least in part, upon therecognition of the various shortcomings of prior art gypsum wallboardand/or cementitious backerboard sheets, and the further recognition thatthe use of aerated concrete as the core material overcomes a number ofthe shortcomings. As it is also known autoclaved aerated concrete is ahigh-quality, load-bearing, as well as insulating building materialproduced in a wide range of product sizes and strengths. The materialhas been used successfully in Europe and is now among widely used wallbuilding materials in Europe with increasing market shares in othercountries.

[0039] Aerated concrete is a steam cured mixture of sand or pulverizedfuel ash, cement, lime and an aeration agent. High pressure steam curingin an autoclave produces a physically and chemically stable product withan average density being about one fifth that of normal concrete. Thematerial includes non-connecting air cells, and this gives aeratedconcrete some of it its unique and advantageous properties. Aeratedconcrete enjoys good strength, low weight, good thermal insulationproperties, good sound deadening properties, and has a high resistanceto fire.

[0040] Aerated concrete may be used in the form of panels or individualbuilding blocks. It has been used for residences; commercial, industrialand agricultural buildings; schools; hospitals; etc. and is a goodmaterial in most all climates. Panels or blocks may be joined togetherusing common mortar or thin set glue mortar or adhesive. Aeratedconcrete has durability similar to conventional concrete or stone and aworkability perhaps better than wood. The material can be cut or sawnand readily receives expandable fasteners. Aerated concrete has athermal conductivity six to ten times better than conventional concrete.The material is also non-rotting, non-toxic and resistant to termites.

[0041] As disclosed in U.S. Pat. No. 4,902,211 to Svanholm, for example,aerated concrete may typically be produced as follows. One or severalsilica containing materials, such as sand, shale ashes or similarmaterials, as well as one or more calcareous binders, such as limeand/or cement, are mixed with a rising or aeration agent. The aerationagent typically includes aluminum powder which reacts with water todevelop hydrogen gas at the same time a mass of what can be considered acalcium silicate hydrate forms. The development of hydrogen gas givesthe mass macroporosity. The rising mass is typically contained within amold. After rising, the mass is permitted to stiffen in the mold forminga semiplastic body which has low strength, but which will keep togetherafter removal from the mold.

[0042] After a desired degree of stiffness is achieved and the body isremoved from the mold, the body may typically be divided or cut by wiresinto separate elements having the desired shape, such as building blocksor larger building panels. The divided body is positioned in anautoclave where it is steam cured at high pressure and high temperatureto obtain suitable strength. The body is then advanced to a separationstation where the adjacent building blocks or panels are separated fromone another. The blocks are packaged, such as onto pallets for storageand transportation.

[0043] Referring now initially to FIGS. 1-5 a wallboard sheet 30 inaccordance with the present invention is now described. The wallboardsheet 30 may be used to form part or all of an interior wall structure,such as the right hand portion of the wall structure 25 (FIG. 1). Ofcourse, the wallboard sheet 30 could be used for ceilings, interiorpartitions, elevator shafts, etc, as will be appreciated by thoseskilled in the art. The wall structure 25 will typically include a frame26 formed of horizontal and vertical wall studs or members, 27, 28,respectively, to which the wallboard sheets 30 are secured by suitablefasteners and/or adhesive.

[0044] The wallboard sheet 30 includes a core 40 having opposing firstand second major surfaces 40 a, 40 b, respectively, and at least oneface layer on at least one of the first and second major surfaces of thecore. The core 40 includes aerated concrete. The provision of aeratedconcrete for the core provides many key advantages over conventionalwallboard sheets, such as gypsum wallboard, for example. The core 40 maybe produced from a mixture of Portland cement, quick lime, sand,aluminum powder and water, although at least some of the sand andperhaps some of the quick lime can be replaced by flyash. In general,the flyash may be used as at least a partial replacement for sand in themix, but flyash, depending on its composition, may react with thealuminum powder in a manner similar to quick lime to produce themicro-cellular bubbles in the expanded aerated concrete.

[0045] In the first embodiment of the wallboard sheet 30, both first andsecond face layers 42 a, 42 b, respectively, are adhesively secured tothe opposing first and second major surfaces 40 a, 40 b of the core 40via respective adhesive layers 43 a, 43 b. In other embodiments, theadhesive may be incorporated into the face layers and/or the surfaceportion of the aerated concrete core as will be appreciated by thoseskilled in the art. One or both of the face layers 42 a, 42 b maycomprise paper, having colors and/or weights, for example, similar toconventional gypsum wallboard paper.

[0046] The core 40 and hence the wallboard sheet 30 may have a generallyrectangular shape defining a pair of opposing side edges 31 a, 31 b,respectively, and a pair of opposing end edges 32 a, 32 b, respectively.The first face layer 42 a may extend around the opposing side edges 31a, 31 b as shown perhaps best in the enlarged cross-sectional view ofFIG. 3. In addition, the opposing end edges 32 a, 32 b of the core maybe exposed (FIG. 2). If desired, a tape, not shown, may be provided onthe opposing ends 32 a, 32 b as will be appreciated by those skilled inthe art.

[0047] The aerated concrete core 40 may have a relatively low density ina range of about 25 to 40 lbs./ft.³ The core 40 and hence the sheet 30,as well, may also have a thickness T in a range of about ¼ to 1 inch, awidth W in a range of about three to five feet, and a length L in arange of about five to sixteen feet. Accordingly, even a 1 inch thick, 4foot by 8 foot wallboard sheet 30 may have a relatively low total weightof about 60 pounds.

[0048] Referring now more particularly to the embodiment of thewallboard sheet 30′ shown in FIGS. 4 and 5, other aspects of theinvention are now explained. The illustrated wallboard sheet 30′includes beveled portions 35 a, 35 b formed on the first major surface40 a′ of the core 40′ adjacent respective opposing side edges 31 a′, 31b′. The beveled portions 35 a, 35 b may facilitate the receipt of tapingand joint compound to cover the joints between adjacent sheets 30′ inthe finished wall structure.

[0049] As perhaps best shown in FIG. 5, the illustrated embodiment ofthe wallboard sheet 30′ also includes only a single face layer 42 a′,although in other embodiments, a second face layer may be applied aswell. In addition, the illustrated embodiment of the core 40′ includesschematically illustrated reinforcing fibers 46. The fibers 46 may beprovided by a fibrous material, such as cellulose or other natural orsynthetic fibers, including fiberglass, metal or other materials, toimpart strength to the core and reduce the relative brittleness of theaerated concrete.

[0050] Another aspect of the wallboard sheet 30′ is that it includes ajoint schematically illustrated by the dashed line 37 extending acrossthe width of the sheet as may be formed during the manufacturing thereofand as will be explained in greater detail herein. The joint 37 can bestronger than the adjacent core material, and without compromising theability to score and snap break the wallboard sheet 30′ as convenientlyas with conventional gypsum wallboard. Stated slightly differently, someembodiments of the wallboard sheet 30′ may include first and secondportions on opposite sides of the joint 37 aligned in end-to-endrelation at respective opposing edges thereof, and an adhesive layer maybe used to join the opposing edges of the first and second portionstogether.

[0051] The other elements of the wallboard sheet 30′ indicated withprime notation and not specifically mentioned are similar to thoseelements described above with reference to the wallboard sheet 30described above. Accordingly, these elements need no further discussionherein. Those of skill in the art will also appreciate that the variousfeatures of the embodiments of the wallboard sheets 30, 30′ can be mixedand/or substituted in yet further embodiments of the invention.

[0052] Because of the relative light weight of the wallboard sheets 30,30′ including aerated concrete, shipping, handling, and installation ata job site are facilitated. In addition, the substitution of aeratedconcrete for gypsum, for example, also offers the advantages ofincreased fire resistance, thermal insulation, sound deadening, andother properties in a wall structure formed by fastening the aeratedconcrete wallboard sheets to a suitable building frame.

[0053] Returning again briefly to FIG. 1 and additionally to FIGS. 6-9,a backerboard sheet 60 in accordance with the present invention is nowdescribed. More particularly, as shown in the left hand portion of FIG.1, the backerboard sheets 60 may be used where the wall is likely to beexposed to splashing water or moisture, such as a bathroom, and otherindoor areas as will be appreciated by those skilled in the art. Thebackerboard sheet 60 is also typically used as an underlayment substratefor decorative area tile 50 and/or border tile 51 as shown in the lefthand portion of FIG. 1. Adjacent ones of the tiles 50, 51 typicallyinclude grout lines 52, 53 therebetween through which moisture maypenetrate. In addition, cracks may form in the grout lines or the tilesthemselves through which moisture may also penetrate.

[0054] Conventional gypsum greenboard or cementitious sheets for suchhigh-moisture applications suffer a number of significant shortcomingsand disadvantages as highlighted in the background of the inventionsection above. The backerboard sheet 60 including a core 70 comprisingaerated concrete, and at least one moisture-resistant face layerovercomes these shortcomings and disadvantages.

[0055] In the first illustrated embodiment of the backerboard sheet 60,both first and second moisture-resistant face layers 72 a, 72 b,respectively, are secured to the opposing first and second majorsurfaces 70 a, 70 b of the core 70. Each moisture-resistant face layer72 a, 72 b illustratively includes a woven fiber mesh 74 a, 74 bincorporated into a respective resin layer 73 a, 73 b. The fibers mayinclude at least one of glass, plastic, and metal. Themoisture-resistant face layer may have other constructions and be formedof different moisture-resistant materials, such as those commonly usedfor cementitious backerboard, and others as will be appreciated by thoseskilled in the art. For example, moisture resistant face layers includenylon, aramid resin, or metal fibers as disclosed in U.S. Pat. No.5,221,386 may also be used, and the entire contents of this patent areincorporated herein by reference.

[0056] The core 70 and hence the backerboard sheet 60 may also have agenerally rectangular shape defining a pair of opposing side edges 61 a,61 b, respectively, and a pair of opposing end edges 62 a, 62 b,respectively. The first face layer 72 a may also extend around theopposing side edges 61 a, 61 b as shown perhaps best in the enlargedcross-sectional view of FIG. 7. In addition, the opposing end edges 72a, 72 b of the core may be exposed (FIG. 6). If desired, a tape, notshown, may be provided on the opposing ends 62 a, 62 b as will beappreciated by those skilled in the art. In addition, the aeratedconcrete core 70 may have the same characteristics and sizes asmentioned above with respect to the wallboard sheets 30, 30′, forexample.

[0057] Referring now more particularly to the embodiment of thebackerboard sheet 60′ shown in FIGS. 8 and 9, other aspects of theinvention are now explained. The illustrated backerboard sheet 60′includes beveled portions 65 a, 65 b formed on the first major surface70 a′ of the core 70′ adjacent respective opposing side edges 61 a′, 61b′. The beveled portions 65 a, 65 b may facilitate the receipt of tapingand sealing or joint compound to cover the joints between adjacentsheets 60′ in the finished wall structure.

[0058] As perhaps best shown in FIG. 9, the illustrated embodiment ofthe backerboard sheet 60′ also includes only a single moisture-resistantface layer 72 a′, although in other embodiments, a second face layer maybe applied as well. The moisture-resistant face layer 72 a′ is alsoillustratively directly secured to the core 70, although an incorporatedresin or adhesive may be used in other embodiments.

[0059] The illustrated embodiment of the core 70′ includes schematicallyillustrated reinforcing fibers 76. The fibers 76 may be provided by afibrous material, such as cellulose or other natural or syntheticfibers, including fiberglass, metal or other materials, to impartstrength to the core and reduce the relative brittleness of the aeratedconcrete. The fibers may also be desirably selected to avoid attractingor retaining moisture.

[0060] Another aspect of the backerboard 60′, similar to the wallboard30′ discussed above, is that it includes a joint schematicallyillustrated by the dashed line 67 extending across the width of thesheet as may be formed during the manufacturing thereof and as will beexplained in greater detail herein. The joint 67 can also be strongerthan the adjacent core material, and without compromising the ability toscore and snap break the backerboard sheet 60′. In other words, thebackerboard sheet 60′ may include first and second portions on oppositesides of the joint 67 aligned in end-to-end relation at respectiveopposing edges thereof, and an adhesive layer may be used to join theopposing edges of the first and second portions together.

[0061] The other elements of the backerboard sheet 60′ indicated withprime notation and not specifically mentioned are similar to thoseelements described above with reference to the backerboard sheet 60described above. Accordingly, these elements need no further discussionherein. Those of skill in the art will also appreciate that the variousfeatures of the embodiments of the wallboard sheets 60, 60′ can be mixedand/or substituted in yet further embodiments of the invention. Becauseof the relative light weight of the backerboard sheets 60, 60′ includingaerated concrete, shipping, handling, and installation at a job site arefacilitated.

[0062] Turning now additionally to the flowcharts of FIGS. 10-13 variousmethod aspects for making the wallboard and/or backerboard sheets inaccordance with the invention are now described. The method may includeforming core material having opposing first and second major surfacesand comprising aerated concrete, securing at least one face layer on atleast one of the first and second major surfaces of the core material,and cutting the core material and at least one face layer securedthereto into a plurality of wallboard or backerboard sheets. Theprovision of aerated concrete for the core provides many key advantagesover conventional gypsum wallboard sheets, and/or conventionalbackerboard sheets, such as gypsum greenboard or cementitiousbackerboard, for example.

[0063] In one class of embodiments, the method may further comprisecuring the core material prior to securing the at least one face layerthereto. In another class, the method may further comprise curing thecore material after securing the at least one face layer thereto.

[0064] Referring now to the flowchart of FIG. 10, a particularlyadvantageous embodiment is described wherein curing is performed beforeadding the at least one face layer. In particular, from the start (Block100), the materials for making aerated concrete are mixed and dispensedinto a suitable mold at Block 102. The materials are permitted to riseand stiffen into a body (Block 104), and the body may then be removedfrom the mold (Block 106). The body having a size of about twenty feetin length, four feet in height, and two feet in width is cured at Block108, such as by positioning in an autoclave as will be appreciated bythose skilled in the art. The one or more face layers can then besecured to the cured sheets of the core material at Block 110.Thereafter, the core material with the face layer(s) secured thereto canbe cut to the desired lengths to form the wallboard or backerboardsheets at Block 112 before packaging/shipping (Block 114) and stoppingor ending the method at Block 116.

[0065] In other words, in this embodiment forming the core materialcomprises dispensing materials for making aerated concrete into a moldand allowing the materials to rise and stiffen into a body, curing thebody, and dividing the cured body into a plurality of cured sheets toserve as the core material. The plurality of the cured sheets may bejoined together in end-to-end relation while advancing the cured sheetsalong a path of travel. In addition, securing the at least one facelayer may be performed while the cured sheets are advanced along thepath of travel.

[0066] A variation of this method embodiment is now explained withreference to the flowchart of FIG. 11. In this embodiment, primenotation is used to indicated similar steps which need no furtherexplanation. In accordance with the illustrated embodiment of FIG. 11,the body is divided, but not separated or cut, into sheets at Block 105,and is then cured at Block 107. Thereafter, the cured sheets are used asthe core material and to which the face layer(s) are secured asdescribed above. This embodiment may offer the advantage of slightlyeasier cutting of the body, since it has not been fully cured; however,the ultimate dimensional accuracy of the sheets may be less compared tofirst curing the body and then cutting the body into cured sheets. Ofcourse, a combination of some cutting or shaping before curing andfurther cutting or shaping after curing are also contemplated by thepresent invention.

[0067] Referring now more particularly to the flow charts of FIGS. 12and 13, the second class of method embodiments, wherein the one or moreface layers are added before final curing, are now described. It isnoted that final curing using a conventional autoclave may placerelatively difficult requirements on the characteristics of the facelayers in terms of temperature resistance and/or abrasion resistance.Accordingly, manufacturing speed or efficiency may need to be consideredin view of the increased face layer material costs as will beappreciated by those skilled in the art.

[0068] The first embodiment is now described with reference to theflowchart of FIG. 12. From the start (Block 130), the materials formaking aerated concrete are mixed and dispensed into a suitable mold atBlock 132. The materials are permitted to rise and stiffen into a body(Block 134), and the body may then be removed from the mold and dividedinto uncured sheets (Block 136). The one or more face layers may besecured to the uncured sheets at Block 138, which can then be cured(Block 140), before being cut into desired lengths at Block 142. Thefinal sheets may be packaged and shipped at Block 144 before stopping orending the method at Block 146. Of course, the final curing could alsobe performed prior to the cutting into individual sheets as will beappreciated by those skilled in the art.

[0069] Referring now to the flowchart of FIG. 13, yet another embodimentof the method is now described. This embodiment is directed to a morecontinuous manufacturing operation. More particularly, from the start(Block 150) the materials for making aerated concrete are dispensed inslurry form onto at least one face layer (Block 152), typically as theface layer is advanced along a conveyor, for example. The slurry mayalternatively be dipensed onto a surface, e.g. a stainless steelsurface, instead of directly onto the face layer. The dwell time on theconveyor may desirably be sufficient to allow the materials to rise andstiffen, and optionally cured, (Block 154) before cutting into finallengths (Block 156). Thereafter, the sheets may be packaged and shippedat Block 158 before stopping (Block 160). Of course in otherembodiments, it is also possible to cut the core material before finalcuring. This may be especially desirably where conventional autoclavecuring is performed which may require a relatively long dwell time inthe heated chamber. However, other curing techniques, such as theaddition of microwave radiation are also contemplated which may providefor near continuous curing of the core material as will also beappreciated by those skilled in the art.

[0070] Of course, in all of the specifically described and contemplatedmethod embodiments, the securing of the at least one face layer maycomprise securing first and second face layers on respective first andsecond major surfaces of the core material. The at least one face layermay comprise paper, such as for a wallboard. Alternately, the at leastone face layer may be moisture-resistant for a backerboard. Forming mayalso include forming the first major surface of the core material tohave beveled portions adjacent respective opposing longitudinal sideedges. In addition, the at least one face layer may be secured to extendaround the opposing longitudinal side edges by the use of simple edgewrapping guides, for example. The core material may also be formed withreinforcing fibers in the aerated concrete.

[0071] Turning now additionally to FIGS. 14-18 various aspects of asystem for making the wallboard and/or backerboard including aeratedconcrete in accordance with the invention are now described. Startingwith the overall simplified schematic diagram of FIG. 14 an illustratedembodiment of the system 200 is now described. The system 200 includes amixer 210 for mixing materials for making aerated concrete. The mixer210 is supplied with the starting materials for making aerated concretefrom the cement supply 201, the sand (ash) supply 202, the water supply203, the aluminum or other aeration agent supply 204, the lime supply205, and the optional reinforcing fiber supply 206. The system alsoillustratively includes at least one face layer supply 215, a former 220downstream from the mixer 210 and connected to the face layer supply215. A cutter 225 is provided downstream from the former 220. And anoptional packager 230 is provided, such as to package the wallboard orbackerboard sheets onto pallets for shipping, for example.

[0072] The former 220 is for forming core material having opposing firstand second major surfaces and comprising aerated concrete, and forsecuring at least one face layer from the at least one face layer supply215 onto at least one of the first and second major surfaces of the corematerial. As described below, in one class of embodiments, the former220 may further include an autoclave for curing the core material priorto securing the at least one face layer thereto. In another class, theformer may further include an autoclave or other curing apparatus forcuring the core material after securing the at least one face layerthereto.

[0073] One particularly advantageous embodiment of the system will nowbe explained with reference to the more detailed schematic diagram ofthe former 220 as shown in FIG. 15. More particularly, the illustratedembodiment of the former 220 may include a mold 240 downstream from themixer for receiving the materials for making aerated concrete thereinand allowing the materials to rise and stiffen into a body 242. Theformer 220 also includes the autoclave 243 downstream from the mold 240for curing the body 242. Of course, the system would also include thenecessary material handling mechanisms and apparatus to remove the body242 and position it as will be appreciated by those skilled in the art.

[0074] The former 220 also includes a divider downstream from theautoclave for dividing the cured body 242 into a plurality of curedsheets to serve as the core material. One or more band saws 245, forexample, could be used to slice the cured body 242 into a plurality ofcured sheets 244. Other types of saws could also be used.

[0075] The former 220 may also include a conveyor 247 and a sheethandler 246 cooperating therewith for joining a plurality of the curedsheets 244 together in end-to-end relation while advancing the curedsheets along a path of travel on the conveyor. Alternatively, the curedsheets 244 may not be joined together, but may have already been cut indesired dimensions. The schematically illustrated end-to-end joiner 250can provide the adhesive, alignment and compressive forces, if needed toinsure a quality joint. Downstream from the joiner 250, a trim/bevelstation 252 can be used to trim the upper and/or side surfaces of thesheets, and also to form the desired beveled sides if desired.

[0076] Both the joiner 250 and trim/bevel station 252 can be readilymade from conventional equipment and need no further discussion herein.What is noted, however, is that the aerated concrete is readily workableunlike conventional concrete, for example. A waste collection system mayalso be provided to collect and recycle trimmed or cut material from theaerated concrete as will be appreciated by those skilled in the art.

[0077] Downstream from the trim/bevel station 252, the former 220 alsoillustratively includes a securing station 253 to apply the one or moreface layers from the appropriate supplies 254, 255. This securingstation 253 can use conventional layer handling, guiding rolls, etc. toattach the at least one face layer while the cured sheets 244 areadvanced along the path of travel. The securing station 253 can alsoinclude the necessary guides and rolls to roll a face layer around thelongitudinal side edges as described above.

[0078] Turning now briefly to FIG. 16 a variation of the formerembodiment described above will now be described. In this embodiment ofthe former 220′, the body 242′ is cut or divided into sheets 244′ beforepositioning in the autoclave 243′. As discussed above, while the cuttingmay be somewhat easier, and a more simple wire saw 249′ may be used, theresulting dimensions of the sheets may not be as accurate. Thisembodiment does, however, avoid the need for higher temperaturecompatible/resistant face layers. Of course, combinations of pre-cureand post-cure shaping of the core material may also be used.

[0079] Turning now more particularly to FIG. 17 another variation orembodiment of a former 220″ is now described. In this embodiment, theface layers from the supplies 254″, 255″ are added downstream fromdividing the body 242″ into uncured sheets 244″ but before positioningin the autoclave 243″ for curing. As noted above this may increase therequirements and costs for the face layers, but may provide increasedmanufacturing efficiencies as will be appreciated by those skilled inthe art. As shown, uncured sheets 244″ may also be passed through cutter225″ prior to the autoclave 243″. Of course, the various core shapingoperations may also be performed on the uncured sheets to form bevelededges, etc.

[0080] A further embodiment of the former 220′″ is described withreference to FIG. 18. This embodiment of the system may provide for nearcontinuous production. In this embodiment, the former 220′″ may comprisea slurry dispenser (and spreader) 260 and a conveyor 247′″ cooperatingtherewith for dispensing the materials for making aerated concreteadjacent at least one face layer, such as from supply 254′″, as the atleast one face layer is advanced along a path of travel. The securingstation 253′″ secures the second face layer from the supply 255′″ andmay wrap the edges in the illustrated embodiment. Again, the slurry mayalso be dispensed directly onto a surface, such as a stainless steelsurface, instead of onto the at least one face layer, with the first andsecond face layers being secured by the securing station 253′″thereafter. In this embodiment, the autoclave or other curing station243′″ is downstream from the dispenser for curing the materials formaking aerated concrete. The autoclave 243′″ may preferably be after thecutter 225′″, for example, but the autoclave or other curing device maybe positioned along the conveyor 247′″. Typically, curing takes between4 and 12 hours at a temperature of about 165° C. and pressure of about150 psi. It is expected that the time from pouring the mixture onto theconveyor to cutting the sheet into final lengths will vary between 20and 50 minutes depending on the relative percentage of cement, lime andaluminum.

[0081] In any of the embodiments, the former may secure first and secondface layers on respective first and second major surfaces of the corematerial. For wallboard sheets, the at least one face layer supply maycomprise at least one paper face layer supply. For backerboard sheets,the at least one face layer supply preferably comprises at least onemoisture-resistant face layer supply.

[0082] Other related concepts and features are disclosed in thefollowing copending patent applications filed concurrently herewith andassigned to the assignee of the present invention and are entitledWALLBOARD SHEET INCLUDING AERATED CONCRETE CORE, attorney work docketnumber 64901; SYSTEM FOR MAKING WALLBOARD OR BACKERBOARD SHEETSINCLUDING AERATED CONCRETE, attorney work docket number 64907; andBACKERBOARD SHEET INCLUDING AERATED CONCRETE CORE, attorney work docketnumber 64908, the entire disclosures of which are incorporated herein intheir entirety by reference.

[0083] It is also contemplated that the wallboard and backerboard sheetsdescribed herein may be produced without the face layers if sufficientstrength and surface smoothness can be obtained by use of the fibrousfiller material alone, for example. However, it is recognized that anyfiller material will add weight and that the volume of fibrous materialis a trade off with weight and strength or flexibility. Thus, it may bedesirable to use just enough fibrous material to produce some slightflexibility without addressing surface smoothing. Accordingly, manymodifications and other embodiments of the invention will come to themind of one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is to be understood that the invention is not to belimited to the specific embodiments disclosed, and that othermodifications and embodiments are intended to be included within thescope of the appended claims.

That which is claimed is:
 1. A method for making wallboard orbackerboard sheets comprising: forming core material having opposingfirst and second major surfaces and comprising aerated concrete;securing at least one face layer on at least one of the first and secondmajor surfaces of the core material; and cutting the core material andat least one face layer secured thereto into a plurality of wallboard orbackerboard sheets.
 2. A method according to claim 1 further comprisingcuring the core material prior to securing the at least one face layerthereto.
 3. A method according to claim 1 further comprising curing thecore material after securing the at least one face layer thereto.
 4. Amethod according to claim 1 wherein forming the core material comprises:dispensing materials for making aerated concrete into a mold andallowing the materials to rise and stiffen into a body; curing the body;and dividing the cured body into a plurality of cured sheets to serve asthe core material.
 5. A method according to claim 4 further comprisingjoining a plurality of the cured sheets together in end-to-end relationwhile advancing the cured sheets along a path of travel.
 6. A methodaccording to claim 5 wherein securing the at least one face layer isperformed while the cured sheets are advanced along the path of travel.7. A method according to claim 1 wherein forming the core materialcomprises: dispensing materials for making aerated concrete into a moldand allowing the materials to rise and stiffen into a body; dividing thebody into a plurality of uncured sheets; and curing the sheets to serveas the core material.
 8. A method according to claim 7 furthercomprising joining a plurality of the cured sheets together inend-to-end relation while advancing the cured sheets along a path oftravel.
 9. A method according to claim 8 wherein securing the at leastone face layer is performed while the cured sheets are advanced alongthe path of travel.
 10. A method according to claim 1 wherein formingthe core material comprises: dispensing materials for making aeratedconcrete into a mold and allowing the materials to rise and stiffen intoa body; and dividing the body into a plurality of uncured sheets toserve as the core material.
 11. A method according to claim 10 furthercomprising curing the uncured sheets after securing the at least oneface layer thereto.
 12. A method according to claim 11 wherein thecuring is after cutting.
 13. A method according to claim 1 whereinforming the core material comprises mixing and dispensing the materialsfor making aerated concrete in slurry form.
 14. A method according toclaim 13 wherein securing the at least one face layer comprisesreceiving the aerated concrete in slurry form thereon as the at leastone face layer is advanced along a path of travel.
 15. A methodaccording to claim 14 further comprising: permitting the aeratedconcrete material to rise and stiffen prior to cutting; and curing theaerated concrete after cutting.
 16. A method according to claim 1securing the at least one face layer comprises securing first and secondface layers on respective first and second major surfaces of the corematerial.
 17. A method according to claim 1 wherein the at least oneface layer comprises paper.
 18. A method according to claim 1 whereinthe at least one face layer is moisture-resistant.
 19. A methodaccording to claim 1 further comprising forming the first major surfaceof the core material to have beveled portions adjacent respectiveopposing longitudinal side edges.
 20. A method according to claim 1wherein securing the at least one face layer comprises securing the atleast one face layer to extend around the opposing longitudinal sideedges.
 21. A method according to claim 1 wherein forming the corematerial comprises forming the core material with reinforcing fibers inthe aerated concrete.
 22. A method for making wallboard or backerboardsheets comprising: dispensing materials for making aerated concrete intoa mold and allowing the materials to rise and stiffen into a body;curing the body; dividing the cured body into a plurality of curedsheets to serve as core material having opposing major surfaces;securing at least one face layer on at least one of the first and secondmajor surfaces of the core material; and cutting the core material andat least one face layer secured thereto into a plurality of wallboard orbackerboard sheets.
 23. A method according to claim 22 furthercomprising joining a plurality of the cured sheets together inend-to-end relation while advancing the cured sheets along a path oftravel.
 24. A method according to claim 23 wherein securing the at leastone face layer is performed while the cured sheets are advanced alongthe path of travel.
 25. A method according to claim 22 securing the atleast one face layer comprises securing first and second face layers onrespective first and second major surfaces of the core material.
 26. Amethod according to claim 22 wherein the at least one face layercomprises paper.
 27. A method according to claim 22 wherein the at leastone face layer is moisture-resistant.
 28. A method according to claim 22further comprising forming the first major surface of the core materialto have beveled portions adjacent respective opposing longitudinal sideedges.
 29. A method according to claim 22 wherein securing the at leastone face layer comprises securing the at least one face layer to extendaround the opposing longitudinal side edges.
 30. A method according toclaim 22 further comprising adding reinforcing fibers to the aeratedconcrete.
 31. A method for making wallboard or backerboard sheetscomprising: dispensing materials for making aerated concrete into a moldand allowing the materials to rise and stiffen into a body; dividing thebody into a plurality of uncured sheets; curing the uncured sheets toserve as core material having opposing first and second major surfaces;securing at least one face layer on at least one of the first and secondmajor surfaces of the core material; and cutting the core material andat least one face layer secured thereto into a plurality of wallboard orbackerboard sheets.
 32. A method according to claim 31 furthercomprising joining a plurality of the cured sheets together inend-to-end relation while advancing the cured sheets along a path oftravel.
 33. A method according to claim 32 wherein securing the at leastone face layer is performed while the cured sheets are advanced alongthe path of travel.
 34. A method according to claim 31 securing the atleast one face layer comprises securing first and second face layers onrespective first and second major surfaces of the core material.
 35. Amethod according to claim 31 wherein the at least one face layercomprises paper.
 36. A method according to claim 31 wherein the at leastone face layer is moisture-resistant.
 37. A method according to claim 31further comprising forming the first major surface of the core materialto have beveled portions adjacent respective opposing longitudinal sideedges.
 38. A method according to claim 31 wherein securing the at leastone face layer comprises securing the at least one face layer to extendaround the opposing longitudinal side edges.
 39. A method according toclaim 31 further comprising adding reinforcing fibers to the aeratedconcrete.
 40. A method for making wallboard or backerboard sheetscomprising: dispensing materials for making aerated concrete into a moldand allowing the materials to rise and stiffen into a body; dividing thebody into a plurality of uncured sheets having opposing first and secondmajor surfaces to serve as the core material; securing at least one facelayer on at least one of the first and second major surfaces of the corematerial; cutting the core material and at least one face layer securedthereto into a plurality of uncured wallboard or backerboard sheets; andcuring the uncured wallboard or backerboard sheets.
 41. A methodaccording to claim 40 wherein the at least one face layer comprisesfirst and second face layers on respective first and second majorsurfaces of the core material.
 42. A method according to claim 40wherein the at least one face layer comprises paper.
 43. A methodaccording to claim 40 wherein the at least one face layer ismoisture-resistant.
 44. A method according to claim 40 furthercomprising forming the first major surface of the core material to havebeveled portions adjacent respective opposing longitudinal side edges.45. A method according to claim 40 wherein the at least one face layerextends around the opposing longitudinal side edges.
 46. A methodaccording to claim 40 further comprising adding reinforcing fibers tothe aerated concrete.
 47. A method for making wallboard or backerboardsheets comprising: mixing and dispensing materials for making aeratedconcrete adjacent at least one face layer advancing along a path oftravel; permitting the aerated concrete materials to rise and stiffen todefine core material having first and second opposing surfaces with theat least one face layer secured thereto; cutting the core material andat least one face layer secured thereto into a plurality of uncuredwallboard or backerboard sheets; and curing the uncured wallboard orbackerboard sheets.
 48. A method according to claim 47 wherein the atleast one face layer comprises first and second face layers onrespective first and second major surfaces of the core material.
 49. Amethod according to claim 47 wherein the at least one face layercomprises paper.
 50. A method according to claim 47 wherein the at leastone face layer is moisture-resistant.
 51. A method according to claim 47further comprising forming the first major surface of the core materialto have beveled portions adjacent respective opposing longitudinal sideedges.
 52. A method according to claim 47 wherein the at least one facelayer extends around the opposing longitudinal side edges.
 53. A methodaccording to claim 47 further comprising adding reinforcing fibers tothe aerated concrete.
 54. A method for making at least one of awallboard or backerboard sheet comprising: forming a core havingopposing first and second major surfaces and at least one face layerthereon, said core comprising aerated concrete.
 55. A method accordingto claim 54 wherein the at least one face layer comprises first andsecond face layers on respective first and second major surfaces of thecore.
 56. A method according to claim 54 wherein the at least one facelayer comprises paper.
 57. A method according to claim 54 wherein the atleast one face layer is moisture-resistant.
 58. A method according toclaim 54 wherein the core has a generally rectangular shape defining apair of opposing side edges and a pair of opposing end edges.
 59. Amethod according to claim 58 wherein the first major surface has beveledportions adjacent respective opposing side edges.
 60. A method accordingto claim 58 wherein the at least one face layer extends around theopposing side edges.